Photon Momentum: The Impact of Light on Movement in Space

In summary, the momentum of photons can create impact forces, as seen in the principle behind solar sails and the cause of the Pioneer anomaly. When photons hit an object, the change in momentum can result in movement in the opposite direction. This has been utilized in spacecrafts and there are current efforts to use it for interstellar travel.
  • #1
Ebi
13
3
TL;DR Summary
Can momentum of photons create impact forces?
We know that photons (light) are massless but they have momentum. Now suppose I am in the space far away from planets/stars that there is no external force exerts on me, if:
1- I turn on a flashlight (torch), would I be pushed in the opposite direction which the flashlight is facing (Newton's third law)?
2- If a star is shedding light on me (its photons hit my body), would I start moving due the impact of photos?
 
Physics news on Phys.org
  • #2
Yes. That's the principle behind solar sails. Also what was deemed to be the cause of the Pioneer anomaly.
 
  • Like
Likes Klystron, vanhees71 and Ebi
  • #3
Ebi said:
Summary:: Can momentum of photons create impact forces?

We know that photons (light) are massless but they have momentum. Now suppose I am in the space far away from planets/stars that there is no external force exerts on me, if:
1- I turn on a flashlight (torch), would I be pushed in the opposite direction which the flashlight is facing (Newton's third law)?
2- If a star is shedding light on me (its photons hit my body), would I start moving due the impact of photos?
Yes, momentum is momentum and it's conserved!
 
  • Like
Likes Vanadium 50 and vanhees71
  • #4
Yes, the momentum of a photon is given by h/lambda. And when the photon hits you and reflects back, the change in the momentum of photon is given by 2h/lambda (assuming normal incidence), you would start moving forward with that momentum.
The momentum of photons (from sunlight) have been used in the past to propel spacecraft s and are called as solar sails. There are efforts currently by breakthrough initiatives, to use ground based laser source to propel light sails to the exoplanet Alpha Centauri. Follow this link to learn more about that.
 

FAQ: Photon Momentum: The Impact of Light on Movement in Space

1. What is photon momentum?

Photon momentum is the amount of momentum carried by a photon, which is a particle of light. It is a measure of the force that a photon exerts on an object when it interacts with it.

2. How does light affect movement in space?

Light can affect movement in space through its momentum. When light hits an object, it transfers some of its momentum to that object, causing it to move. This is known as radiation pressure and can be observed in phenomena such as solar sails.

3. How is photon momentum related to the speed of light?

Photon momentum is directly proportional to the speed of light. This means that the faster a photon is moving, the more momentum it has. As the speed of light is constant, the momentum of a photon is also constant.

4. Does photon momentum have a direction?

Yes, photon momentum has a direction. The direction of photon momentum is always in the same direction as the photon's movement. This means that when light is reflected or refracted, its momentum also changes direction.

5. How is photon momentum measured?

Photon momentum can be measured using a device called a photodetector. This device can detect the amount of energy transferred from a photon to an object, which is then used to calculate the momentum of the photon. Other methods, such as measuring the deflection of charged particles by a magnetic field, can also be used to measure photon momentum.

Back
Top